Fabric softener compositions have been in commercial use for many years as treatments for laundered fabrics. Fabric softeners are generally employed as dryer-added sheets or as rinse-added fabric softeners. Fabric softeners impart favorable properties to the fabric such as enhanced softness, increased fluffiness, reduced levels of static electricity and easier ironing.
A modern laundering process utilizing an automatic washing machine typically washes laundry in four stages. During the first stage, a wash cycle, the laundry is agitated in water containing a detergent. Next, during a first spin cycle, wash liquor is removed and the laundry is spun to remove excess water. This cycle is followed by a rinse cycle where the washing machine tub is filled with clean water, a rinse-added fabric softener is optionally added, and the laundry is again agitated. A final spin cycle removes the rinse liquor and the laundry is again spun to remove excess water. Following the laundering process, the laundry is either hung until dry or placed in an automatic dryer, optionally adding a dryer-added fabric softener sheet to the dryer.
Rinse-added fabric softeners are generally dilute aqueous suspensions or dispersions of cationic softening agents such as quaternary ammonium compounds. Typically, the quaternary ammonium compounds are salts of the formula: ##STR1## where R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are lipophilic organic substituents and X is a halogen. The positively charged cation is readily adsorbed onto surfaces of fabric being laundered. This deposition of the cation onto the fabric imparts enhanced softness to the fabric and diminishes the static electricity built up on the fabric surface.
Dryer-added sheets also employ quaternary ammonium salts to enhance softness and reduce the level of static electricity. In manufacturing the sheets, the quaternary ammonium salts are sprayed or coated onto a non-woven fabric, or they are added directly to the formulation used to make the non-woven fabric.
Several attempts have been made to enhance the softness and anti-static properties of rinse-added fabric softener through the addition of polymeric compounds.
British Patent No. 1,549,180 to Dumbrell et al. teaches a composition useful for treating fabric in the final rinse of the laundering process. This composition contains a cationic quaternary ammonium compound with one or more long chain alkyl groups, and a silicone compound, such as a linear fluorinated polysiloxane. Through the use of this linear silicone compound, it is purported that in addition to fabric softening benefits, this compound also imparts the benefits of easier ironing, anti-static properties, and soil resistant properties.
U.S. Pat. No. 4,908,140 to Bausch et al. reports a similar composition as that reported in Dumbrell et al. However, Bausch et al. found that through the use of an aqueous emulsion of a highly branched or crosslinked silicone polymer, as compared to the linear compounds of Dumbrell et al., the rewettability of fabrics was enhanced in addition to the softness.
U.S. Pat. No. 4,326,965 discloses a liquid fabric softening composition containing a cationic fabric softening agent and a polymeric additive such as polyethylene glycol with a molecular weight of 6,000. By the inclusion of polyethylene glycol, fabric softening compositions are prepared that are water-dispersable and pourable and can be more easily dispensed by an automatic dosing device into the rinse cycle on an automatic washing machine. No change in softening properties was reported.
Japanese Patent Application J 89-023585-B addresses the problem of inferior softening and anti-static performance of fabric softeners on synthetic fibers as compared to cotton fibers. By using a softening composition containing cationic surfactant, such as a quaternary ammonium salt, and a carboxylic acid type anionic compound, the deposition of the quaternary ammonium salt onto synthetic fibers is increased. This softening composition containing the carboxylic acid type anionic compound is reported to lead to equivalent softening and antistatic properties on synthetic fibers as prior known compositions led to with cotton fibers. No improvement was reported for cotton fabrics. In addition, unlike the polymers used in the compositions of the present invention, many of the polymers used in Japanese Patent Application J 89-023585-B are not compatible with rinse-added fabric softener compositions.